1. Field of the Invention
The present invention relates to a data communications method and apparatus, and particularly to a data communications method and apparatus for transmission and reception of voice data and ordinary data for high-level data link control (HDLC).
2. Description of the Related Art
As shown in FIG. 1, a conventional example of data communications apparatus of this type consists of, on the transmission side, a data analyzer 800 that separates HDLC data and voice data, a frame generator 810 and an FCS adder 830 that generate frames from the HDLC data, a voice frame generator 820 that generates frames from voice data, and a frame transmitter 840 that transmits both types of frames to a transit trunk 890; and on the reception side, a frame detector 850 that receives frames, a frame analyzer 860 that separates the received frames into voice frames and HDLC frames, a voice data frame extractor 870 that extracts data from voice frames, and an HDLC frame check circuit 880 that extracts data from HDLC frames (for example, as disclosed in Japanese Patent Laid-open No. 173943/83).
Next will be explained the operation of this prior art example.
In contrast to general HDLC data, voice data do not need to be repeated when transmitting voice data between packet exchanges that transmit data according to high-level procedures (HDLC), and error check blocks FCS(Frame Check Sequence) are therefore not necessary. Here, as shown in FIG. 2, in contrast to general HDLC frames that are composed of flag pattern F, address part A, control information part C, a data part (user's data), error check block FCS, voice frames are made up of flag pattern F, address part A', a data part (user's data).
As shown in FIG. 1, when transmitting HDLC frames mixed with voice frames, the data to be transmitted is separated on the transmitting side into HDLC data and voice data at data analyzer 800, frames are generated from the voice data at voice frame generator 820, frames are generated from the HDLC data at HDLC frame generator 810, FCS code is added at FCS adder 830, and voice frames or HDLC frames are sequentially transmitted from frame transmitter 840.
On the reception side, address A or A' of the received frames is analyzed at frame analyzer 860 and separated into voice frames and HDLC frames, and voice data are extracted from the voice frames at voice data frame extractor 870. HDLC frames are checked at HDLC frame check circuit 880 and after processing by protocol such as repeating, data are extracted.
In such a conventional data communications apparatus, because voice data are also transmitted as packets, transmission of voice data in response to a generated request must wait until completion of transmission of an HDLC frame being transmitted. In particular, there is the problem that a long portion of HDLC user data will involve a lengthy transmission time for the HDLC frame, thereby resulting in a lengthy waiting time for transmission of a voice frame.